Minimum leaf gap, IMRT parameters (DMPO), Pinnacle v9.0

[Rick Sims (ADHB)]

Dear list,

 

How does Pinnacle take into account the minimum leaf gap setting under IMRT parameters?

 

I’ve noticed that Pinnacle often produces segments where the minimum leaf gap is less than the entered value and wondered how the system is actually using this information.

 

Maybe its a statistical based approach (in that Pinnacle aims to ensure the minimum leaf gap set by the user is achieved for 95% of the segments produced) or is it just ignoring my request?!

 

Replies on or off list appreciated.

 

Thanks,

Rick

 

 

Rick Sims

Physicist (Radiation Oncology)

Tel: +64 (0)9 307 4949 ext. 6210

Fax: +64 (0)9 307 8975

Email: ri...@adhb.govt.nz

 

[Sam Painter]

Hi Rick,
Not in front of a station but perhaps this will help guide you.

In 9.0, dynamic and static minimum leaf gaps have been separated. The
static one is used in DMPO. The others in sliding windows (and
presumably SmartArc)

These are set in physics, under MLC options I think. In planning, I'm
not sure what you are looking at (again not at a station) but in 8.0
you could set the min gap in the sliding windows converter. Perhaps
you are looking at a parameter that belongs to SmartArc??

There were circumstances (7.4f) where violations could occur when
using differing decimal places for jaws vs mlc for Varian machines. I
haven't tried in 8.0 or up. I use 1 decimal for both and 0 for the min
static leaf gap for a millenium mlc (USE AT YOUR OWN RISK - COULD
CRASH LEAVES ON MARK-2). DMPO likes to work in 5 mm jaw position and 1
mm leaf position resolutions. If you are fixing your own jaws with 2
decimal positions, not sure how it would behave but it may trickle
over to the MLC gaps (especially under the jaws).

Hope this helps,
Sam Painter
St George Cancer Care Centre
Kogarah, NSW

> Email: ri...@adhb.govt.nz<mailto:ri...@adhb.govt.nz>